OUTFLOWS AND DEEP-WATER PRODUCTION BY MARGINAL SEAS

We examine some of the processes that determine the properties of marg inal sea outflows by reviewing historical data and by an analysis of t wo simple models. Our numerical simulation model makes several of the streamtube approximations of SMITH (1975), but goes on to include a Fr oude number-dependent entrainment parameterization, an Ekman number-de pendent parameterization of broadening, and it can accept real bottom topography and real oceanic temperature and salinity profiles. This nu merical model reproduces some of the main features of the four major o utflows considered here (Mediterranean Sea, two from the Norwegian-Gre enland Sea, and Weddell Sea) including the bulk properties of the prod uct water. A notable feature of these four outflows is that the densit y ordering of the source waters and product waters is reversed; for ex ample, the densest source water comes from the Mediterranean Sea, and yet the Mediterranean outflow makes the least dense product water. The reason is that intense entrainment of North Atlantic Central Water de creases the density of the Mediterranean outflow by about 1kg m-3 as i t begins to descend the continental slope. The three high-latitude out flows are more or less similar in that strong entrainment generally oc curs over short segments of the path where the bottom topography is re latively steep, typically just beyond the shelf-slope break. However, the densities of these outflows are decreased much less by entrainment (about 0.1 kg m-3 in the Denmark Strait outflow, about 0.2kg m-3 in t he Faroe Band Channel outflow and 0.03kg M-3 in the Weddell Sea outflo w) as they descend to the bottom in their respective basins. Entrainme nt causes much less decrease in density in these outflows primarily be cause of the lower density differences between these outflows and thei r overlying oceanic waters. High latitude outflows are more likely to reach the bottom because the oceanic water column in polar and subpola r seas is weakly stratified. These and other results indicate that the temperature and salinity of the oceanic water column are of considera ble importance in determining the product water of a marginal sea outf low. Numerical experiments suggest that the density of the product wat er is remarkably insensitive to variations in the density of the sourc e water. For example, if the density of the Mediterranean source water is arbitrarily increased by 1 kg m-3, then the increased density diff erence between outflow and overlying oceanic water results in even mor e vigorous entrainment. This increases the transport of product water by about 10(6)M3s-1 and limits the increase in density of the product water to only about 0.15kg M-3. These and other results are obtained a lso from a simple end-point model of a descending outflow.